Liquid chromatography (LC) is a technique for performing analytical or preparative separation of a liquid-phase sample material of interest (e.g., a mixture of different chemical compounds) into constituent components. During the course of a chromatographic separation, the sample material is transported in a mobile phase (typically one or more solvents). The sample/mobile phase is forced through a stationary phase that is immiscible with the mobile phase. Typically, the stationary phase is provided in the form of a mass of particles (a packing or bed) supported in a column or cartridge through which the sample flows. The column bed is typically retained at each end of the column by a frit or filter that allows the sample/mobile phase to flow through while preventing the packing material from escaping the column. The inlet end of the column is connected to an inlet conduit by which the sample/mobile phase is introduced into the column. A mobile phase reservoir, a pump and a sample injector are located upstream of the inlet end and interconnected to the inlet end via the inlet conduit. The outlet end of the column is connected via an outlet conduit to a suitable detector or other destination. In the column, the respective compositions of the mobile phase and stationary phase are selected to cause differing components of the sample material in the column to become distributed between the mobile phase and stationary phase to varying degrees dependent on the respective chemistries of the sample material's components. Components that are strongly retained by the stationary phase travel slowly with the mobile phase, while components that are weakly retained by the stationary phase travel more rapidly. As a result, components of differing compositions become separated from each other as the mobile phase flows through the column. In this manner, the components are in effect sorted sequentially as the eluent flows out from the column, thereby facilitating their analysis by the detector or otherwise isolating components of interest from other components of the original sample material.
Conventionally, the inside wall surface of an LC column is made as smooth as possible. This also means that the inside surface remains at a constant radial position relative to the column center (the central axis through the column) over the length of the column, such that the inside surface is parallel to the net fluid flow direction through the column. In other words, the wall defining the interior of the column is a straight cylindrical bore. This conventional configuration allows the particles to move easily along the inside wall surface during packing of the column and during any resettling of the column during the packing process. The disadvantage of this approach is that the packed particles are very ordered at and near the column wall while they are more randomly packed away from the column wall. As particles are packed into the column, they are forced outward toward the column wall. The restriction presented by the column wall thus results in a large number of particles being aligned at the same radial position from the column center. This leads to differing flow rates near and far from the column walls. This flow heterogeneity increases the rate of analyte dispersion and consequently reduces resolution of the detected peaks eluted from the column.
Therefore, there is a need for LC columns structured to reduce position-dependent flow heterogeneity in the columns.